Photoelectrochemical quantification of electron transport resistance of TiO2 photoanodes for dye-sensitized solar cells

Abstract

A simple photoelectrochemical method is developed to measure the intrinsic electron transport resistance (R₀) of TiO₂ photoanodes. R₀ is considered as the sum of electron transport resistance at the TiO₂/FTO interface and among TiO₂ nanoparticulates during electron transport process, which is independent of the manner of electron injection, its physical and chemical environments. Because TiO₂ photoanodes are the common electron transport pathways for dye-sensitized solar cells (DSSCs) process and the photoelectrocatalytic oxidation process, R₀ can be also considered as a quantitative measure of the electron transport resistance of the photoanodes in the DSSC process. The proposed method will provide a simple and rapid alternative to quantitatively evaluate the quality of the TiO₂ photoanodes for DSSCs using R₀ values. A series of TiO₂/FTO photoanodes with different electron transport resistance were fabricated using conventional screen-printing technique, surface modifications using titanium organic sol and TiCl₄ aqueous solution. R₀ values of the photoanodes were characterized and subsequently used to correlate with the important performance parameters of the corresponding DSSCs. The preliminary results suggest that these surface modifications do not significantly affect the surface area, film thickness, dye loading and optical properties of the TiO₂ film, but significantly decrease the R₀ values. Furthermore, the DSSCs photoanodes with lower R₀ values due to the organic sol or TiCl₄ modification bestow better photovoltaic performance than the corresponding non-modified photoanodes. Therefore, it can be concluded that the performance improvements were mainly attributed to the decrease of the R₀ values, which validates the proposed electrochemical evaluation method.